"""Synthetic ninlight OTA images: 56-byte W600 header + gzip stream + 512-byte NINL trailer.

The layout mirrors ninlight-firmware/tools/mkimage/nl_mkimage.py and was checked against a real
image (spec §2). Tests build their own images instead of copying firmware binaries.
"""

from __future__ import annotations

import gzip
import hashlib

CONTENT_WITH_SSID = b"\x00boot\x00ninIOT\x00ninlight-%s\x00"
CONTENT_WITHOUT_SSID = b"\x00boot\x00ninlight-%s\x00"


def build_payload(content: bytes) -> bytes:
    return b"\xab" * 56 + gzip.compress(content, mtime=0)


def build_image(
    device_type: str = "gu10_rgb",
    version: str = "0.3.8-47-g71a57",
    *,
    content: bytes = CONTENT_WITH_SSID,
    payload: bytes | None = None,
    magic: bytes = b"NINL",
    fmt: int = 1,
    corrupt_hash: bool = False,
) -> bytes:
    body = payload if payload is not None else build_payload(content)
    trailer = bytearray(b"\xff" * 512)
    trailer[0:4] = magic
    trailer[4] = fmt
    trailer[5:21] = device_type.encode().ljust(16, b"\x00")
    trailer[21:37] = version.encode().ljust(16, b"\x00")
    trailer[37:69] = bytes(32) if corrupt_hash else hashlib.sha256(body).digest()
    return body + bytes(trailer)